It consists more precisely of the development of a complete method for treating CO2 coming from oxycombustion (combustion with pure oxygen or with a gas leaner in nitrogen than air is) of an industrial nature, enabling it to be packaged for transport and storage for various uses.
In point of fact, gases from the combustion of fossil fuels and/or biomass or from waste incineration or gases from glass furnaces mainly contain heavy metals such as mercury, arsenic, iron, nickel etc, organic contaminants and compounds of the SOx or NOx type.
Solutions exist for treating contaminants at atmospheric pressure for which atmospheric discharges are regulated (SO2, NOx, Hg and CO for example).
For example, document EP-A-1 332 786 describes a method for the purification of a gas stream by eliminating NOx, SOx, Hg, and HgO by oxidation with ozone.
In addition, it is known from document EP-A-1 308 198 to eliminate mercury by gas-liquid contact in the presence of H2S. Flash distillation of the liquid phase provides a gas rich in mercury that is trapped by adsorption on Al2O3, TiO2, SiO2, active carbon or zeolite, doped with sulfur-containing compounds.
However, these methods do not guarantee complete elimination of the contaminants treated but aim at a limited content discharged to atmosphere, such as required by the specifications in place.
In addition, they treat fumes from combustion with air, which are less concentrated since they mainly contain nitrogen. In point of fact, if the stoichiometry of combustion reactions is considered, the quantity of oxygen (oxidant) to be provided is determined by the quantity of fuel. Therefore, if air is used and not pure oxygen, given that there is only 21% oxygen in this air, it is necessary to enter a much higher flow in order to guarantee an identical concentration of oxygen so as to carry out this combustion under correct conditions. Thus, the streams are more dilute and nitrogen is therefore found in a large quantity in the fumes since it is the main component of air (˜78%).
However, the application for capturing and storing CO2 coming from oxycombustion creates supplementary requirements for purification from other compounds and/or these same compounds in different proportions.
In point of fact, this application for capturing and storing CO2 coming from oxycombustion requires not only treatment to remove large quantities of compounds that are not in the majority, but also a thorough purification treatment (“polishing”) for the product that aims at eliminating impurities that are prejudicial to all the method as well as to the storage of this CO2 in suitable geological strata.
In particular, water must be stopped to concentration such that its presence does not present a blocking problem, either in the case of low temperature treatment <0° C. or during transport or storage of CO2.
Starting from this, a problem presented is to provide an improved method for the purification of a gas stream containing CO2, namely a method guaranteeing intensive elimination of the contaminants treated, in particular intensive elimination of water.